1. Field of the Invention
The present invention relates to footwear. The invention concerns, more particularly, athletic shoes having one or more support elements with a mechanism for varying the stiffness characteristics of the sole.
2. Description of Background Art
Modern articles of athletic footwear include a highly-refined combination of elements that each perform a specific function directed toward maximizing athletic performance. The two primary elements of athletic footwear are an upper and a sole. The upper is formed of leather, synthetic materials, or a combination thereof and comfortably receives the foot while providing ventilation and protection from the elements. The sole includes multiple layers that are conventionally referred to as an insole, midsole, and outsole. The insole is a thin, padded member located adjacent to the foot that improves the comfort of the footwear. The midsole forms the middle layer of the sole and often incorporate a resilient foam material, such as polyurethane, phylon, or ethyl vinyl acetate, that attenuates shock and absorbs energy when the footwear makes contact with the ground. The outsole is fashioned from a durable, wear resistant material, such as carbon-black rubber compound, and includes a textured lower surface to improve traction.
An alternate midsole design, disclosed in U.S. Pat. Nos. 5,353,523 and 5,343,639 to Kilgore et al., and hereby incorporated by reference, includes four foam columns placed between rigid top and bottom plates. FIG. 1 depicts a similar, commercially-available article of footwear 10 that includes an upper 12 which is attached to a sole structure 14. Sole structure 14 incorporates an outsole 16 and a midsole 18 that includes four elastomeric support elements 20, a semi-rigid heel plate 22, a base plate 24, and a midfoot wedge 26. In addition, midsole 18 may include a cushioning layer located above heel plate 22 that extends throughout the longitudinal length of footwear 10 and enhances the comfort of footwear 10.
Support elements 20 are the primary component that attenuates shock and absorbs energy when footwear 10 initially contacts the ground in the heel area, during walking or running, for example. Each support element may include a band 28 circumscribing the outer surface and may have an interior void that extends longitudinally from the upper to lower surface. The compliance of each support element 20 may be altered by repositioning band 28. For example, each support element 20 may be configured for greatest compliance by positioning band 28 adjacent either the top or bottom. Least compliance is achieved by centrally-locating band 28, as depicted in FIG. 1. By altering the compliance of support elements 20, an individual may configure footwear 10 to have proper shock attenuation and energy absorption for the particular weight of the individual. In addition, alterations in the compliance of support elements 20 may be utilized to configure footwear 10 for differing activities or playing surfaces. The present invention relates to an alternate method of altering the compliance of support elements, such as support elements 20.